As well known, quality of wireless communication in trains will be affected a lot due to increasing high-speed mobility of trains. High-speed mobility will lead to the following problems for wireless communication.                UE in service stays in an individual cell for shorter time;        Doppler shift will increase delay of UE handover so that handover can't be finished in one individual cell;        Frequently handover will lead to bad user experience.        
As a result, how to minimize the bad impact caused by high-speed mobility is very necessary, especially for the handover issues.
The existing solution, as shown in FIG. 1, called “large cell solution” to reduce the handover times is that the cells along railways are configured into one specific network (i.e. only serve for the users in the railways) and also increase coverage of one individual cell with remote base station, which may still have the following problems.                Low capacity. Large cell solution has the same capacity as the normal cell, but its coverage is large. So the average capacity per square meter is relative lower than normal cell.        Low spectrum efficiency. As well known, spectrum is very significant resource for the Operators. If coverage area of the whole network is certain, the larger the coverage for the whole spectrum is, the lower the spectrum efficiency is.        Inconvenient for Network Expansion. The configuration of the large cell solution is set at the beginning of the network planning. If expanse of the network is needed, Hardware of base stations has to be reinstalled.        